Electrochromic compound, electrochromic composition, and display element

ABSTRACT

To provide an electrochromic compound, represented by the following general formula (I): General Formula (I) where X 1 , X 2 , X 3 , X 4 , X 5 , X 6 , X 7  and X 8  are each independently a hydrogen atom or a monovalent substituent; R 1  and R 2  are each independently a monovalent substituent; A− and B− are each independently a monovalent anion; and Y is represented by the following general formula (II) or (III): General Formula (II) General Formula (III) where X 9 , X 10 , X 12 , X 13 , X 14 , X 15 , X 16 , X 17 , and X 18  are each independently a hydrogen atom or a monovalent substituent.

TECHNICAL FIELD

The present invention relates to an electrochromic compound, and anelectrochromic composition, both of which colors in cyan as they arecolored, and relates to a display element using the electrochromiccompound or the electrochromic composition.

BACKGROUND ART

As for an electronic medium replacing paper, developments of electronicpaper have been recently actively carried out.

The electronic paper has characteristics that the display device thereofis used like paper, and therefore requires properties different fromconventional display devices, such as CRT and LCD. For example, requiredproperties thereof are being a reflective a display device as well ashaving high white reflectance and high contrast ratio, being able todisplay with high definition, giving the display a memory function,being driven at low voltage, being thin and light, and beinginexpensive. Among them, as properties associated with a quality of adisplay, particularly white reflectivity and contrast ratio close tothat of paper, and color display are highly demanded.

Previously, as for a display device for use as electronic paper, forexample, proposed are a system using reflecting liquid crystals, asystem using electrophoresis, a system using toner migration, and thelike. In any of these systems, however, it is very difficult to performmulticolor display with maintaining white reflectivity and contrastratio. In order to perform multicolor display, color filters aretypically provided. When color filters are provided, the color filtersthemselves absorb light to thereby reduce reflectance. Moreover, use ofthe color filters requires to divide one pixel into three, red (R),green (G), and blue (B), reflectance of a display device reduces. Alongthe reduction in the reflectance of the display device, the contrastratio thereof also reduces. When the white reflectivity and contrastratio are significantly reduced, the visibility becomes very poor, andtherefore it is difficult to use such device as electronic paper.

PTL 1 and PTL 2 each disclose a reflecting color display medium, in anelectrophoresis element of which color filters are formed, but it isclear that such display medium cannot provide excellent image qualityeven when color filters are formed in the display medium of low whitereflectivity and a low contrast ratio. Moreover, PTL 3 and PTL 4 eachdisclose an electrophoresis, with which color display is realized bymoving particles, which are tinted in a plurality of colors.Theoretically, use of this method does not lead to a solution for theaforementioned problems, and cannot realize both high white reflectivityand a high contrast ratio.

Meanwhile, as a promising technology for realizing a reflecting displaydevice without providing color filters as described above, there is asystem using electrochromic phenomenon. The phenomenon where, as voltageis applied, an oxidation-reduction reaction is reversibly causeddepending on the polarity to thereby reversibly change color is calledelectrochromism. A display device utilizing coloring/bleaching (may alsostated as coloring and bleaching hereinafter) of an electrochromiccompound which cases this phenomenon is an electrochromic displaydevice. Since this electrochromic display device is a reflecting displaydevice, has a memory effect, and can be driven at low voltage,researches and developments of electrochromic devices have been widelyconducted from a development of materials and designing of devices, as apromising option for a display device technology for electronic paper.

However, as the electrochromic display device performs coloring andbleaching using an oxidation-reduction reaction, the electrochromicdisplay device has a disadvantage that a coloring-bleaching responsespeed is slow. PTL 5 discloses an example, in which an improvement ofthe coloring-bleaching response speed is attempted by fixing anelectrochromic compound adjacent to an electrode. According to thedescriptions in PTL 5, although the time required for coloring andbleaching is conventionally about 10 seconds, the time required fromcolorless to color in blue and the time required from blue to colorlessare both improved to about 1 second. However, this is not necessarilysufficient. As for the researches and developments of electrochromicdisplay devices, further improvements of the coloring-bleaching responsespeed are necessary.

An electrochromic display device can display various colors depending ona structure of an electrochromic compound used as a display material,and therefore it is hoped to be used as a multicolor display device.Especially as the electrochromic display device can reversibly changeits colorless state to the color state, a laminate multicolor structurecan be realized. In the color display of the laminate structure, it isnot necessary to divide one pixel into three, red (R), green (G), andblue (B), as in the conventional technology. Therefore, there areadvantages that the reflectance and contrast ratio of the display deviceare not reduced.

There are several conventional examples of a multicolor display deviceutilizing such electrochromic display device. For example, PTL 6discloses a multicolor display device, in which particles of a pluralityof electrochromic compounds are laminated. In PTL 6, disclosed is anexample of a multicolor display device, in which a plurality ofelectrochromic compounds, which are high molecular compounds havingfunctional groups, each of which requires different voltage to color,are laminated to form a multicolor display electrochromic compound.

Moreover, PTL 7 discloses a display device, in which multipleelectrochromic layers are formed on an electrode to display multiplecolors utilizing a difference in voltage or current required for color.In PTL 7, disclosed is an example of a multicolor display device, whichcolors different colors, and has a display layer formed by laminating ormixing a plurality of electrochromic compounds each require differentthreshold voltage and electric charge to color.

PTL 8 discloses an electrochromic device in which a full-color displayis realized by laminating a plurality of structural units each formed bysandwiching an electrolyte layer containing an electrochromic compound.Moreover, PTL 9 discloses an example of a multicolor display devicecorresponding to RGB 3 colors, in which a passive matrix panel andactive matrix panel are composed of electrochromic elements, in each ofwhich an electrolyte layer containing at least one electrochromiccompound is present. Furthermore, PTL 10 discloses that coloringproperties and durability are improved by a reversible recordingmaterial, in which one, or two or more compounds having the specificstructure are contained on surfaces of metal oxide particles. Moreover,PTL 11 discloses an electrochromic compound having a pyridine ring, andrepresented by the certain structural formula, which can color in yellowand can be bleached. Furthermore, PTL 12 disclosed phthalic acid-basedcompounds which colors in yellow, magenta, and cyan.

The viologen-based organic electrochromic compounds disclosed in PTL 5,PTL 6, and PTL 7 are compounds having high stability and high durabilityfor repetitive use, but they display colors, such as blue, and green,not 3 primary colors, yellow, magenta, and cyan, required for formationof full color. Moreover, the styryl-based dyes listed in PTL 8, PTL 9,and PTL 10 display excellent yellow, magenta, and cyan, but these dyeshave problems in stability of coloring and bleaching, or durability forrepetitive use.

Moreover, PTL 11 is related to the compound, which colors in yellow andis bleached, not cyan. The phthalic acid-based compound disclosed in PTL12 has a problem that such compound has a poor memory function.

As mentioned above, an ideal electrochromic compound for realizingfull-color electronic paper has not been provided, and it is desired toprovide the material having excellent color tone, durability, andstability.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-161964

PTL 2: JP-A No. 2004-361514

PTL 3: JP-A No. 2004-520621

PTL 4: JP-A No. 2004-536344

PTL 5: JP-A No. 2001-510590

PTL 6: JP-A No. 2003-121883

PTL 7: JP-A No. 2006-106669

PTL 8: JP-A No. 2003-270671

PTL 9: JP-A No. 2004-151265

PTL 10: JP-A No. 2008-122578

PTL 11: JP-A No. 2011-102382

PTL 12: JP-A No. 2006-71767

SUMMARY OF INVENTION Technical Problem

The present invention aims to provide an electrochromic compound, whichexhibits sharp light absorption spectrum characteristic as colored,colors in vivid cyan, and exhibits less remained color as bleached.

Solution to Problem

As for the means for solving the aforementioned problems, theelectrochromic compound of the present invention is represented by thefollowing general formula (I):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇ and X₈ are each independently ahydrogen atom or a monovalent substituent; and R₂ are each independentlya monovalent substituent; A⁻ and

B⁻ are each independently a monovalent anion; and Y is represented bythe following general formula (II) or (III);

where X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆, X₁₇, and X₁₈ are eachindependently a hydrogen atom or a monovalent substituent.

Advantageous Effects of Invention

The present invention can solve the aforementioned various problems inthe art, and can provide an electrochromic compound, which exhibitssharp light absorption spectrum characteristic as colored, colors invivid cyan, and exhibits less remained color as bleached.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram illustrating a structural example of atypical display element using the electrochromic compound of the presentinvention.

FIG. 1B is a schematic diagram illustrating a structural example of atypical display element using the electrochromic compound of the presentinvention.

FIG. 2 is a schematic diagram illustrating a structural example of theelectrochromic compound of the present invention.

FIG. 3 is a schematic diagram illustrating another structural example ofa typical display element using the electrochromic composition of thepresent invention.

FIG. 4 is a diagram depicting absorption spectrums of the displayelectrode of Example 1, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 5 is a diagram depicting a color value of the electrochromicdisplay element produced in Example 1.

FIG. 6 is a diagram depicting absorption spectrums of the displayelectrode of Example 3, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 7 is a diagram depicting absorption spectrums of the displayelectrode of Example 4, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 8 is a diagram depicting absorption spectrums of the displayelectrode of Example 10, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 9 is a diagram depicting absorption spectrums of the displayelectrode of Example 11, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 10 is a diagram depicting absorption spectrums of the displayelectrode of Example 12, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 11 is a diagram depicting absorption spectrums of the displayelectrode of Example 13, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 12 is a diagram depicting absorption spectrums of the displayelectrode of Example 14, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 13 is a diagram depicting absorption spectrums of the displayelectrode of Example 15, on which the electrochromic display layer isformed, in the bleached state and the colored state.

FIG. 14 is a diagram depicting absorption spectrums of the displayelectrodes of Comparative Examples 1 to 3, on each of which theelectrochromic display layer is formed, in the colored state.

FIG. 15 is a diagram depicting absorption spectrums of the displayelectrode of Comparative Example 4, on which the electrochromic displaylayer is formed, in the bleached state and the colored state.

DESCRIPTION OF EMBODIMENTS Electrochromic Compound

The present inventors have diligently conducted studies to solve theaforementioned problems. As a result, it has found out that theaforementioned problems can be solved with an electrochromic compoundrepresented by the following general formula (I). Specifically, theelectrochromic compound represented by the following general formula (I)has sharp light absorption characteristics as colored, colors in cyan,and exhibits less color as bleached.

In the general formula (I), X₁, X₂, X₃, X₄, X₅, X₆, X₇ and X₈ are eachindependently a hydrogen atom or a monovalent substituent; R₁ and R₂ areeach independently a monovalent substituent; A⁻ and B⁻ are eachindependently a monovalent anion; and Y is represented by the followinggeneral formula (II) or (III);

In the general formulae (II) and (III), X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄,X₁₅, X₁₆, X₁₇, and X₁₈ are each independently a hydrogen atom or amonovalent substituent.

In the general formulae (I), (II), and (III), X₁, X₂, X₃, X₄, X₅, X₆,X₇, X₈, X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆, X₁₇, and X₁₈ may be ahydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a cyanogroup, a carboxyl group, a carbonyl group, an alkoxycarbonyl group thatmay have a substituent, an aryloxycarbonyl group that may have asubstituent, an alkylcarbonyl group that may have a substituent, anarylcarbonyl group that may have a substituent, an amide group, anaminocarbonyl group, a monoalkylaminocarbonyl group that may have asubstituent, a dialkylaminocarbonyl group that may have a substituent, amonoarylaminocarbonyl group that may have a substituent, adiarylaminocarbonyl group that may have a substituent, a sulfonic acidgroup, a sulfonyl group, an alkoxysulfonyl group that may have asubstituent, an aryloxysulfonyl group that may have a substituent, analkylsulfonyl group that may have a substituent, an arylsulfonyl groupthat may have a substituent, a sulfone amide group, an aminosulfonylgroup, a monoalkylaminosulfonyl group that may have a substituent, adialkylaminosulfonyl group that may have a substituent, amonoarylaminosulfonyl group that may have a substituent, adiarylaminosulfonyl group that may have a substituent, an amino group, amonoalkylamino group that may have a substituent, a dialkylamino groupthat may have a substituent, an alkyl group that may have a substituent,an alkenyl group that may have a substituent, an alkynyl group that mayhave a substituent, an aryl group that may have a substituent, an alkoxygroup that may have a substituent, an aryloxy group that may have asubstituent, an alkylthio group that may have a substituent, an arylthiogroup that may have a substituent, or a heterocyclic group that may havea substituent.

Use of these groups gives a resulting electrochromic compound solubilityto a solvent, which makes a production process of an element easy.Moreover, it enables to adjust a color spectrum (color).

In the general formula (I), moreover, monovalent groups represented byR₁, and R₂ may be each independently an alkyl group that may have afunctional group, an alkenyl group that may have a functional group, analkynyl group that may have a functional group, or an aryl group thatmay have a functional group.

It is preferred that either R₁ or R₂, or both thereof have a functionalgroup capable of directly or indirectly bonding to a hydroxyl group. Thefunctional group capable of directly or indirectly bonding to a hydroxylgroup is not particularly limited, as long as it is a functional groupcapable of directly or indirectly bonding to a hydroxyl group throughhydrogen bonding, absorption, or a chemical reaction. The structure ofsuch functional group is not limited. Preferable examples thereofinclude: a phosphonic acid group; a phosphoric acid group; a silyl group(or a silanol group), such as a trichlorosilyl group, a trialkoxysilylgroup, a monochlorosilyl group, and a monoalkoxysilyl group; and acarboxyl group.

As for the trialkoxysilyl group, preferred are a triethoxysilyl group,and a trimethoxysilyl group. Among them, particularly preferred are aphosphonic acid group and a silyl group (a trialkoxysilyl group, or atrihydroxysilyl group), as they have high bonding force to anelectroconductive or semiconductive nano structure.

Among electrochromic compounds represented by the general formula (I),the more preferable embodiment thereof is an electrochromic compoundrepresented by the following general formula (IV);

In the general formula (IV), X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, X₁₀, X₁₁,X₁₃ and X₁₄ are each independently a hydrogen atom or a monovalentsubstituent; R₃ is a substituted or unsubstituted alkyl group, or asubstituted or unsubstituted alkoxy group; R₁ and R₂ are eachindependently a monovalent substituent; and A⁻ and B⁻ are eachindependently a monovalent anion.

In the general formulae (I) and (IV), A⁻ and B⁻ are each a monovalentanion, which may be the same or different. The monovalent anionsrepresented by A⁻ and B⁻ are not particularly limited, as long as theyare monovalent anions that stably pair with cation sites. Preferableexamples thereof include Br ion (Br⁻), Cl ion (Cl⁻), ClO₄ ion (ClO₄ ⁻),PF₆ ion (PF₆ ⁻), and BF₄ ion (BF₄ ⁻).

Note that, the electrochromic compound of the present inventionpreferably has X (e.g., X₁, X₂, X₃, X₄, X₅, X₆, X₇, and X₈) and R (e.g.,R₁, and R₂) which makes the general formula (I) a symmetrical structure,in view of easiness of synthesis thereof, and improvement of stabilitythereof. Moreover, the electrochromic compound of the present inventioncolors in cyan, but can color in magenta or yellow due to theaforementioned effect of substituents.

Specific examples of the electrochromic compound of the presentinvention are presented below, but the electrochromic compound of thepresent invention is not limited to these examples. Note that, in thefollowing specific examples, Y in the general formula (I) may be thegeneral formula (II) or the general formula (III).

(Electrochromic Composition)

The electrochromic composition of the present invention contains anelectroconductive or semiconductive nano structure, and theelectrochromic compound (the electrochromic compound represented by thegeneral formula (I)) of the present invention bonded to or adsorbed ontothe nano structure, and may further contain other components, ifnecessary.

In the electrochromic composition of the present invention, theelectrochromic compound is bonded to the electroconductive orsemiconductive nano structure.

When the electrochromic composition of the present invention is used inan electrochromic display element, the resulting electrochromic displayelement colors in cyan, and has excellent memory of an image, i.e.,color image retentiveness. Note that, the electroconductive orsemiconductive nano structure is nano particles, or a nano-orderstructure having surface irregularities, such as a nano porousstructure.

In the case where either R₁ or R₂ or both thereof has a functional groupcapable of directly or indirectly bonding to a hydroxyl group asmentioned above, for example, in the case where the electrochromiccompound of the present invention contains a sulfonic acid group, aphosphoric acid group, or a carboxyl group as a binding or adsorbingstructure, the electrochromic compound easily forms a complex with thenano structure to thereby form an electrochromic composition havingexcellent color image retentiveness. A plurality of the aforementionedsulfonic acid group(s), phosphoric acid group(s), and/or carboxylgroup(s) may be contained in the electrochromic compound. In the casewhere the electrochromic compound of the present invention contains asilyl group or a silanol group, moreover, the electrochromic compoundbonds to the nano structure through a siloxane bond, which forms astrong bond between the electrochromic compound and the nano structure,to thereby provide a stable electrochromic composition. The siloxanebond described herein means a chemical bond via a silicon atom and anoxygen atom. Moreover, the bonding method, embodiments, and the like ofthe electrochromic composition are not particularly limited, providedthat the electrochromic composition has a structure where theelectrochromic compound and the nano structure are bonded with asiloxane bond.

A material for constituting the electroconductive or semiconductive nanostructure is preferably metal oxide in view of its transparency andelectroconductivity. Examples of the metal oxide include metal oxidescontaining, as a main component, titanium oxide, zinc oxide, tin oxide,aluminum oxide (abbrev., alumina), zirconium oxide, cerium oxide,silicon oxide (abbrev., silica), yttrium oxide, boron oxide, magnesiumoxide, strontium titanate, potassium titanate, barium titanate, calciumtitanate, calcium oxide, ferrite, hafnium oxide, tungsten oxide, ironoxide, copper oxide, nickel oxide, cobalt oxide, barium oxide, strontiumoxide, vanadium oxide, aluminosilicate, calcium phosphate, oraminosilicate. These metal oxides may be used alone, or in combinationas a mixture.

Considering electric properties, such as electric conductivity, andphysical properties, such as optical properties, it is possible todisplay in multicolor with excellent coloring-bleaching response speedwhen at least one metal oxide selected from the group consisting oftitanium oxide, zinc oxide, tin oxide, alumina, zirconium oxide, ironoxide, magnesium oxide, indium oxide, and tungsten oxide is used.Especially when titanium oxide is used, multicolor display having evenmore excellent coloring-bleaching response speed is possible.

As for the shape of the metal oxide, preferred are metal oxide particleshaving the average primary particle diameter of 30 nm or smaller. Use ofthe smaller particle diameter thereof improves transmittance of light tothe metal oxide, and realizes use of a shape having a large surface areaper unit (referred to as “specific surface area” hereinafter). Use ofthe metal oxide having a large specific surface area can moreefficiently bear the electrochromic compound thereon, which realizesmulticolor display having excellent display contrast of coloring andbleaching. The specific surface area of the nano structure is notparticularly limited, but, for example, the specific surface areathereof is designed to be 100 m²/g or greater.

(Display Element)

The display element of the present invention contains a displayelectrode, a counter electrode provided to face the display electrodeand to be spaced from the display element, an electrolyte providedbetween the display electrode and the counter electrode, and a displaylayer provided on a surface of the display electrode at the side of thecounter electrode where the display layer contains an electrochromiccompound represented by the general formula (I), and may further containother members, if necessary.

Structural examples of a typical display element using theelectrochromic compound of the present invention are depicted in FIGS.1A and 1B. As illustrated in FIGS. 1A and 1B, the display element 10, 20of the present invention contains a display electrode 1, and a counterelectrode 2 provided to fact the display electrode 1 and to be spacedfrom the display electrode 1, and an electrolyte 3 provided between theboth electrodes (the display electrode 1 and the counter electrode 2),and the display element 10, 20 has a display layer 5 containing at leastthe electrochromic compound 4 a of the present invention on a surface ofthe display electrode 1 at the counter electrode 2 side (the side facingthe counter electrode 2) thereof.

In the display element of 1B, the display layer 5 is formed on a surfaceof the display electrode 1 at the counter electrode 2 side thereof usingthe electrochromic compound 4 a of the present invention. As for theforming method, any of methods, such as immersing, dipping, vapordeposition, spin coating, printing, and inkjet printing, may be used. Inthe case where the molecular structure of the electrochromic compound 4a of the present invention contains an adsorbing group (bonding group) 4c, as illustrated in FIG. 2, the adsorbing group 4 c is adsorbed on thedisplay electrode 1 to form the display layer 5. In this case, asillustrated in FIG. 2, oxidation-reduction coloring section 4 b, whichcolors, is linked with the adsorbing group 4 c via the spacer section 4d, which constitutes the electrochromic compound 4 a. As illustrated in1A, moreover, it is also possible that a solution is formed bydissolving an electrolyte in a solvent, and the electrochromic compound4 a is dissolved in the solution. In this case, the electrochromiccompound 4 a is colored and bleached by an oxidation-reduction reactiononly at a surface of the electrode. Specifically, within the solutioncontaining the electrochromic compound, the surface of the displayelectrode 1 facing the counter electrode 2 functions as a display layer.

Another structural example of a typical display element using theelectrochromic compound of the present invention is depicted in FIG. 3.

The display element 30 of the present invention contains a displayelectrode 1, a counter electrode 2 provided to face the displayelectrode 1 and to be spaced from the display electrode 1, anelectrolyte 3 provided between the both electrodes (the displayelectrode 1 and the counter electrode 2), and a display layer 5containing at least the electrochromic composite 4 e of the presentinvention, which is provided on a surface of the display electrode 1 atthe side of the counter electrode 2. Moreover, the display element 30contains a white reflecting layer 6 formed of white particles providedon a surface of the counter electrode 2 at the side of the displayelectrode 1 (the surface thereof facing the display electrode 1).

In the display element illustrated in FIG. 3, the display layer 5 isformed on a surface of the display electrode 1 at the side of thecounter electrode 2 using the electrochromic composition 4 e of thepresent invention. As for the forming method, any of methods, such asimmersing, dipping, vapor deposition, spin coating, printing, and inkjetprinting, may be used. As illustrated in FIG. 2, the molecular structureof the electrochromic compound 4 a in the electrochromic composition 4 eof the present invention contains a bonding group 4 c, and the bondinggroup 4 c is bonded to the electroconductive or semiconductive nanostructure to constitute the electrochromic composition 4 e. Theelectrochromic composition 4 e is provided as a layer on the displayelectrode 1, to thereby form the display layer 5.

The electrochromic compound in the electrochromic composition of thepresent invention can contain, in the molecular structure thereof, afunctional group capable of directly or indirectly bonding to a hydroxylgroup (adsorbing group), so-called a bonding group, and therefore thebonding group is bonded to the electroconductive or semiconductive nanostructure to constitute the electrochromic composition. Theelectrochromic composition is provided as a layer on the displayelectrode 1 to thereby form the display layer 5.

Materials used for constituting the electrochromic display elements 10,20, and 30 according to the embodiments of the present invention areexplained hereinafter.

As for a material for constituting the display electrode 1, atransparent electric conductive substrate is desirably used. As for thetransparent electric conductive substrate, preferred is a substrate, inwhich a transparent electric conductive film is coated on glass or aplastic film. In the case of the plastic film, a light and flexibledisplay element can be produced.

A material of the transparent electric conductive film is notparticularly limited as long as it is a material having electricconductivity. However, it is necessary to secure transmittance of light.Therefore, use of a transparent electric conductive material, which istransparent and has excellent electric conductivity, is desirable. Useof such material can enhance the visibility of a color to be colored.

As for the transparent electric conductive material, an inorganicmaterial, such as tin-doped indium oxide (abbrev.: ITO), fluorine-dopedtin oxide (abbrev.: FTO), and antimony-doped tin oxide (abbrev.: ATO),can be used, but the transparent electric conductive material isparticularly preferable an inorganic material containing indium oxide(referred to as “In oxide” hereinafter), tin oxide (referred to as “Snoxide” hereinafter), or zinc oxide (referred to as “Zn oxide”hereinafter). The In oxide, Sn oxide, and Zn oxide are materials thatcan be easily formed into a film by sputtering, and also are materialsthat can attain both excellent transparency and electric conductivity.Moreover, the particularly preferable materials are InSnO, GaZnO, SnO,In₂O₃, and ZnO.

Examples of a material for constituting a display substrate (referencenumber is not depicted), on which the display electrode 1 is provided,include glass, and plastic. When a plastic film is used as the displaysubstrate, a light and flexible display element can be produced.

As for the counter electrode 2, a transparent electric conductive filmformed of ITO, FTO, or zinc oxide, an electric conductive metal filmformed of zinc or platinum, or carbon may be used. The counter electrode2 is also typically formed on a counter substrate (reference number isnot depicted). The counter electrode substrate is also preferably glass,or a plastic film. In the case where a metal plate, such as zinc, isused as the counter electrode 2, the counter electrode 2 also functionsas a substrate.

In the case where a material for constituting the counter electrode 2 isa material that induces a reverse reaction, which is reverse to theoxidization-reduction reaction induced by the electrochromic compositionof the display layer, stable coloring and bleaching are possible.Specifically, when a material, which induces a reduction reaction in thecase where the electrochromic composition is colored by oxidization, orinduces an oxidization reaction in the case where the electrochromiccomposition is colored by reduction, is used as the counter electrode 2,reactions of coloring and bleaching in the display layer 5 containingthe electrochromic composition become more stable.

As for a material for constituting the electrolyte 3, a solution inwhich a supporting electrolyte is dissolved in a solvent is typicallyused.

Examples of the supporting electrolyte include: an inorganic ionic salt,such as alkali metal salt, and alkali earth metal salt; quaternaryammonium salt; acid; and alkali. Specific examples thereof includeLiClO₄, LiBF₄, LiAsF₆, LiPF₆, CF₃SO₃Li, CF₃COOLi, KCl, NaClO₃, NaCl,NaBF₄, NaSCN, KBF₄, Mg(ClO₄)₂, and Mg(BF₄)₂.

Moreover, examples of the usable solvent include propylene carbonate,acetonitrile, γ-butyrolactone, ethylene carbonate, sulfolane, dioxolane,tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide,1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, polyethylene glycol, andalcohol.

As the electrolyte is not particularly limited to a fluid electrolyte inwhich a supporting electrolyte is dissolved in a solvent, other than theexamples mentioned above, a gel electrolyte, or a solid electrolyte,such as a polymer electrolyte can also be used. Examples of the solidelectrolyte include a perfluorosulfonic acid-based polymer membrane. Thesolution electrolyte has an advantage that it has high ion conductivity,and the solid electrolyte is suitable for producing an element that doesnot deteriorate and has high durability.

In the case where the display element of the present invention is usedas a reflecting display element, moreover, it is preferred that a whitereflecting layer 6 be provided between the display electrode 1 andcounter electrode 2, as illustrated in FIG. 3. As for the formation ofthe white reflecting layer 6, the simplest production method thereof isdispersing white pigment particles in a resin, and applying theresultant onto the counter electrode 2.

As for the white pigment particles, particles formed of typical metaloxide can be used. Specific examples thereof include titanium oxide,aluminum oxide, zinc oxide, silicon oxide, cesium oxide, and yttriumoxide. Moreover, the electrolyte can be also functioned as a whitereflecting layer by mixing the white pigment particles in a polymerelectrolyte.

As for a driving method of the display elements 10, 20, and 30, anymethod may be used as long as the predetermined voltage and current canbe applied. Use of a passive driving system can produce an inexpensivedisplay element. Moreover, use of an active driving system can performdisplay of high definition and high speed. The active driving can beeasily realized by providing active driving elements on the countersubstrate.

EXAMPLES

The electrochromic compound and electrochromic composition of thepresent invention, and a display element using the electrochromiccompound and electrochromic composition are explained through Examples,but these Examples shall not be construed as to limit the scope of thepresent invention.

Example 1 Synthesis of Electrochromic Compound [Structural Formula (21)]

According the following synthesis flows (a) and (b), the electrochromiccompound represented by the structural formula (21) was synthesized.

<a> Synthesis of Intermediate Product (21-1)

Synthesis Flow (a)

A 100 mL three-necked flask was charged with 0.594 g (3.00 mmol) of2,6-dichloroquinoxaline, 1.72 g (8.4 mmol) of4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine, 0.055 g (0.060mmol) of tris(dibenzylideneacetone)dipalladium(0), and 0.053 g (0.144mmol) of triicyclohexylphosphonium tetrafluoroborate, and was purgedwith argon gas. Thereafter, to the flask, 11 mL of 1,4-dioxane and 8 mLof a 1.27M-tripotassium phosphate aqueous solution, which had beendegassed with argon gas, were added in this order, and the resultant wassubjected to reflux for 4 hours at 100° C. Thereafter, the reactionsolution was cooled to room temperature, and chloroform and a saturatedsalt solution were added to the reaction solution. The resultingsolution was transferred into a separating funnel, and the organic layerwas washed with a saturated salt solution. Thereafter, magnesium sulfateserving as a drying agent was added to the organic layer, and themixture was stirred for 1 hour to remove water. Subsequently, 1 g ofpalladium scavenger silica gel (manufactured by Sigma-Aldrich Japan) wasadded, and the resultant was stirred for 1 hour at room temperature, toremove the palladium remained in the organic layer. After separating thedrying agent and the silica gel through filtration, the solvent wasremoved under the reduced pressure. The resulting crude product waspurified by silica-gel column chromatography (toluene/acetone=½), tothereby obtain a target product (yielded amount: 0.638 g, yield: 75%).

<b> Synthesis of Electrochromic Compound [Structural Formula (21)]

Synthesis Flow (b)

A 25 mL three-necked flask was charged with 0.114 g (0.40 mmol) of2,6-bis(4-pyridyl)-quinoxaline, 0.358 g (1.35 mmol) of4-bromomethylbenzylphosphonic acid, and 3.0 mL of dimethylformamide, andthe resulting mixture was allowed to react for 2 hours at 90° C. Aftercooling the reaction solution to room temperature, the solution wasreleased into 2-propanol. Subsequently, the obtained solids weredispersed in 2-propanol, followed by collecting the solids. Then, thesolids were dried for 2 days at 100° C. under reduced pressure, tothereby obtain a target product (yielded amount: 0.272 g, yield: 85%).

[Production and Evaluation of Electrochromic Display Element] (a)Formation of Display Electrode and Electrochromic Display Layer

First, a glass substrate with FTO electric conductive film in the sizeof 25 mm×30 mm (manufactured by AGC Fabritech Co., Ltd.) was provided.Onto the 19 mm×15 mm region of the top surface of the glass substrate, atitanium oxide nano particle dispersion liquid (SP210, manufactured byShowa Titanium K.K.) was applied by spin coating, followed by performingannealing for 15 minutes at 120° C., to thereby form a titanium oxideparticle film. Onto the titanium oxide particle film, a 1% by mass2,2,3,3-tetrafluoropropanol solution of the compound represented by thestructural formula (21) was applied by spin coating, and the appliedsolution was subjected to annealing for 10 minutes at 120° C., tothereby form a display layer 5 having an electrochromic composition, inwhich the electrochromic compound had been adsorbed on the surfaces ofthe titanium oxide particles.

(b) Formation of Counter Electrode

Separately from the glass substrate, a glass substrate with an ITOelectric conductive film (manufactured by GEOMATEC Co., Ltd.) in thesize of 25 mm×30 mm was prepared and provided as a counter substrate.

(c) Production of Electrochromic Display Element

A cell was produced by bonding the display substrate and the countersubstrate together via a spacer having a thickness of 75 μM.

Next, titanium oxide particles (CR50, manufactured by ISHIHARA SANGYOKAISHA, LTD.) having the primary particle diameter of 300 nm weredispersed, in an amount of 35% by mass, in a solution, in which 20% bymass of tetrabutylammonium perchlorate had been dissolved in dimethylsulfoxide, to thereby prepare an electrolyte solution. The electrolytesolution was then enclosed in the cell, to thereby produce anelectrochromic display element. The structure of electrochromic displayelement is presented in FIG. 3.

[Coloring/Bleaching Test]

The electrochromic display layer formed in Example 1 was placed in aquartz cell. As for a counter electrode, a platinum electrode was used.As for a reference electrode, an Ag/Ag⁺ electrode (RE-7, manufactured byBAS Inc.) was used. The cell was filled with an electrolytic solutionprepared by dissolving 0.1 M of tetrabutylammonium perchlorate indimethyl sulfoxide. To this quartz cell, light was applied from adeuterium tungsten halogen light source (DH-2000, manufactured by OceanOptics, Inc.). The transmitted light was detected by a spectrometer(USB4000, manufactured by Ocean Optics, Inc.), to measure the absorptionspectrum. The absorption spectrums of the bleached state and coloredstate are presented in FIG. 4. In the bleached state before applyingvoltage, there was no absorption in the entire visible region of 400 nmto 700 nm, and the electrochromic display layer was transparent. Whenthe voltage of −1.5 V was applied using a potentiostat (ALS-660C,manufactured by BAS Inc.), the maximum absorption wavelength was 710 nm,and the electrochromic display layer colored in vivid cyan.

The evolution of coloring/bleaching was performed on the electrochromicdisplay element produced in Example 1. The evaluation ofcoloring/bleaching was carried out by applying diffused light using aspectrophotometer MCPD7700, manufactured by Otsuka Electronics Co., Ltd.

In the bleached state before applying the voltage, the electrochromicdisplay element of Example 1 had no color, and was white.

When a voltage of 3.0 V was applied to this display electrode for 2seconds by connecting a negative electrode to the display electrode 1 ofthe display element and connecting a positive electrode to the counterelectrode 2 thereof, the electrochromic display element of Example 1colored in vivid cyan.

The measured color value is depicted in FIG. 5 using CIE LAB scale.

Example 2

An electrochromic compound [the compound represented by the structuralformula (1) listed earlier] was synthesized by allowing the intermediateproduct 22-1 synthesized in Example 1 to react with 2 equivalents ofethyl bromide.

Next, in 2,2,3,3-tetrafluoropropanol, 1% by mass of the synthesizedelectrochromic compound [the compound represented by the structuralformula (1)] and 5% by mass of tetrabutylammonium perchlorate serving asan electrolyte were dissolved, to thereby prepare an electrochromiccompound solution. This electrochromic compound solution was enclosed ina cell prepared by bonding glass substrates each with an ITO electricconductive film in the size of 30 mm×30 mm (manufactured by GEOMATECCo., Ltd.) together as a display substrate and a counter substrate via aspacer having a thickness of 75 μm, to thereby produce an electrochromicdisplay element. The structure of the electrochromic display element ispresented in FIG. 1.

When a voltage of 3 V was applied to the display element produced inExample 2 for 2 seconds, the display element was colored in cyan. When areverse voltage of −2V was applied to the display element for 1 second,the color was bleached and the display element was returned totransparent. It was confirmed that the electrochromic compound of thepresent invention colored in cyan as it was colored, and moreover, nocolor was left as it was bleached.

Example 3

An electrochromic compound (Ex.-3) was synthesized in accordance withthe following scheme.

(a) Synthesis of Intermediate Product(1,5-dimethoxy-2,6-di(4-pyridyl)naphthalene)

A 50 mL-flask was charged with 0.658 g (1.90 mmol) of2,6-dibromol,5-dimethoxynaphthalene, 1.560 g (7.61 mmol) of4-(4,4,5,5-tetramethyl1,3,2-dioxaborolan-2-yl)pyridine, 70 mg (0.076mmol) of tris(dibenzylideneacetone)dipalladium(0), and 67 mg (0.182mmol) of tricyclohexylphosphine tetrafluoroborate, and then purged withargon. Thereafter, 2.16 g of tripotassium phosphate, 7 mL of water, and7 mL of 1,4-dioxane were added to the flask, and the resulting mixturewas heated and stirred for 18 hours at 95° C. After cooling the reactionsolution to room temperature, the precipitated solids were collectedthrough filtration, and then were washed with ethanol and ethyl acetate,to thereby obtain 0.543 g of a target product as colorless crystals.

(b) Synthesis of Electrochromic Compound (Ex.-3)

A 25 mL-flask was charged with 0.539 g (1.57 mmol) of1,5-dimethoxy-2,6-di(4-pyridyl)naphthalene, 1.460 g (5.51 mmol) of4-bromomethylbenzylphosphonic acid, and 19 mL of dimethylformamide, andthe resulting mixture was stirred for 3 hours at 90° C. After coolingthe resulting solution to room temperature, the solution was releasedinto 2-propanol. Subsequently, the obtained solids were collected, tothereby obtain a target product (yielded amount: 1.35 g).

Example 4

An electrochromic compound (Ex.-4) was synthesized in the same manner asin Example 3, provided that 2,6-dibromol,5-dimethoxynaphthalene wasreplaced with 2,6-dibromonaphthalene.

Example 5

An electrochromic compound (Ex.-5) was synthesized in the same manner asin Example 3, provided that 2,6-dibromo-1,5-dimethoxynaphthalene wasreplaced with 2,6-dibromo1,5-dihexydihexenylnaphthalene.

Example 6 Production of Electrochromic Display Element (a) Formation ofDisplay Electrode and Electrochromic Display Layer

First, a glass substrate in the size of 30 mm×30 mm was provided. On the16 mm×23 mm region of the top surface of the glass substrate, an ITOfilm was formed by sputtering so that a thickness thereof was to beabout 100 nm, to thereby form a display electrode 1. A sheet resistancebetween the terminal edges of the display electrode 1 was measured, andthe sheet resistance thereof was about 200Ω.

Next, a titanium oxide nano particle dispersion liquid (SP210,manufactured by Showa Titanium K.K.) was applied onto the glasssubstrate, on which the display electrode 1 had been formed, by spincoating, and the coating liquid was subjected to annealing for 15minutes at 120° C., to form a titanium oxide particle film.Subsequently, a 1% by mass 2,2,3,3-tetrafluoropropanol solution of theelectrochromic compound (Ex.-3) synthesized in Example 3 was applied asa coating liquid by spin coating. The coating liquid was subjected toannealing for 10 minutes at 120° C., to thereby form a display layer 5,in which the electrochromic compound was adsorbed on surfaces of thetitanium oxide particles.

(b) Formation of Counter Electrode

Separately from the glass substrate above, a glass substrate in the sizeof 30 mm×30 mm was provided. On the entire top surface of the glasssubstrate, an ITO film was formed by sputtering so that the thicknessthereof to be about 150 nm. Further, on the top surface of the glasssubstrate on the entire surface of which the transparent electricconductive thin film had been formed, a solution, which had beenprepared by adding 25% by mass of 2-ethoxyethyl acetate to athermocurable electric conductive carbon ink (CH10, manufactured by JUJOCHEMICAL CO., LTD.), was applied by spin coating. The coating solutionwas subjected to annealing for 15 minutes at 120° C., to thereby form acounter electrode 2.

(c) Production of Electrochromic Display Element

A cell was produced by bonding the display substrate 1 and the countersubstrate 2 together via a spacer having a thickness of 75 μm. Next,titanium oxide particles (CR50, manufactured by ISHIHARA SANGYO KAISHA,LTD.) having the primary particle diameter of 300 nm were dispersed, inan amount of 35% by mass, in a solution, in which 20% by mass oftetrabutylammonium perchlorate had been dissolved in dimethyl sulfoxide,to thereby prepare an electrolyte solution. The electrolyte solution wasthen enclosed in the cell, to thereby produce an electrochromic displayelement using the electrochromic compound (Ex.-3).

Example 7 Coloring/Bleaching Test of Produced Electrochromic DisplayElement

A comparative evaluation of coloring and bleaching was performed on theelectrochromic display element produced in Example 6. The evaluation ofcoloring/bleaching was carried out by applying diffused light using aspectrophotometer LCD-5000 manufactured by Otsuka Electronics Co., Ltd.

When a voltage of 3.0 V was applied to this display electrode for 1second by connecting a negative electrode to the display electrode 1 ofthe display element and connecting a positive electrode to the counterelectrode 2 thereof, the electrochromic display element of Example 6colored in excellent cyan.

It was confirmed that the electrochromic compound of Example 3 hadhardly any color in the bleached state, and exhibited clear cyan colorin the colored state.

Moreover, after applying a coloring voltage (3.0 V, 2 seconds), theelectrochromic display element produced in Example 6 remained thecolored state even 300 seconds later from switching off of the power.

The display electrode on which the electrochromic display layer had beenformed in Example 6 was placed in a quartz cell. As for a counterelectrode, a platinum electrode was used. As for a reference electrode,an Ag/Ag⁺ electrode (RE-7, manufactured by BAS Inc.) was used. The cellwas filled with an electrolytic solution prepared by dissolvingtetrabutylammonium perchlorate in dimethyl sulfoxide to give aconcentration of 20% by mass. Light was applied to the quartz cell froma deuterium tungsten halogen light source (DH-2000, manufactured byOcean Optics, Inc.). The transmitted light was detected by aspectrometer (USB4000, manufactured by Ocean Optics, Inc.), to measurethe absorption spectrum. The absorption spectrums of the bleached stateand colored state are presented in FIG. 6. In the bleached state beforeapplying voltage, there was hardly any absorption in the entire visibleregion of 400 nm to 800 nm, and the electrochromic display layer wastransparent. When the voltage of −1.5 V was applied using a potentiostat(ALS-660C, manufactured by BAS Inc.), the maximum absorption wavelengthwas around 650 nm, and the electrochromic display layer colored in vividcyan.

Example 8

An electrochromic display element was produced in the same manner as inExample 6, provided that the compound (Ex.-3) was replaced with thecompound (Ex.-4), and absorption spectrums was measured using a quartzcell in the same manner as in Example 6. The absorption spectrumsthereof are presented in FIG. 7 a. Similarly to the compound (Ex.-3), inthe bleached state before applying voltage, there was hardly anyabsorption in the entire visible region of 400 nm to 800 nm, and theelectrochromic display layer was transparent. When the voltage of −1.5 Vwas applied using a potentiostat (ALS-660C, manufactured by BAS Inc.),the maximum absorption wavelength was around 650 nm, and theelectrochromic display layer colored in vivid cyan.

Example 9

An electrochromic display element was produced in the same manner as inExample 6, provided that the compound (Ex.-3) was replaced with thecompound (Ex.-5), and absorption spectrums was measured using a quartzcell in the same manner as in Example 6. Similarly, in the bleachedstate before applying voltage, there was hardly any absorption in theentire visible region of 400 nm to 800 nm, and the electrochromicdisplay layer was transparent. When the voltage of −1.5 V was appliedusing a potentiostat (ALS-660C, manufactured by BAS Inc.), though it wasnot depicted in the figured, the maximum absorption wavelength wasaround 725 nm, and the electrochromic display layer colored in cyan.

Example 10

Using 0.02 g of 1,5-dihexynyl-2,6-di(4-pyridyl)naphthalene, which wasthe synthesis intermediate product of the electrochromic compound(Ex.-5), 0.04 g of 5% Pd/C (palladium carbon), and 100 mL of toluene,hydrogenation was performed under a flow of hydrogen gas. The obtainedsolids were allowed to react with 4-bromomethylbenzylphosphonic acid, tothereby obtain an electrochromic compound (Ex.-10). The yield was 90%.

Example 11

An electrochromic compound (Ex.-11) was synthesized in the same manneras in Example 3, provided that 2,6-dibromo-1,5-dimethoxynaphthalene wasreplaced with 2,6-dibromo-1,5-di(2-ethylhexyloxy)naphthalene. The yieldwas 72%.

Example 12

An electrochromic compound (Ex.-12) was synthesized as yellow crystalsin the same manner as in Example 3, provided that2,6-dibromo-1,5-dimethoxynaphthalene was replaced with3,7-dibromo-1,5-diphenylnaphthalene. The yield was 70%.

Example 13

A 50 mL-flask was charged with 0.400 g of1,5-trifluoromethanesulfonyloxy-2,6-di(4-pyridyl)naphthalene, 0.315 g of2-methoxyphenylboronic acid, 0.366 g of sodium carbonate, 80 mg oftetrakis triphenylphosphine palladium, 2 mL of water, and 10 mL ofdioxane and was purged with argon. After the resulting mixture wasstirred for 2 hours at 90° C., the mixture was cooled to roomtemperature. Chloroform was added to the mixture, and the resultant wassubjected to filtration with CELITE. After washing the filtrate withwater, the solvent was removed from the filtrate under the reducedpressure, and the residue was washed with ethyl acetate, to therebyobtain 0.205 g of colorless solids.

A 25 mL-flask was charged with 0.100 g of the above-obtained colorlesssolids, 0.160 g of 4-bromomethylbenzylpliosphonic acid, and 3 mL ofN,N-dimethylformamide (DMF), and the resulting mixture was stirred for 3hours at 90° C. under the argon flow. To the resulting reactionsolution, 2-propanol was added, to thereby precipitate yellow solids.The yellow solids were collected by filtration, and dried, to therebyobtain 0.179 g of an electrochromic compound (Ex.-13) as colorlesscrystals. The yield was 86%.

Example 14

An electrochromic compound (Ex.-14) (cream color crystals) wassynthesized in the same manner as in Example 13, provided that2-methoxyphenylboronic acid was replaced with 2,4-difluorophenylboronicacid. The yield was 67%.

Example 15

A 50 mL-flask was charged with 0.300 g of1,5-dihydroxy-2,6-di(4-pyridyl)naphthalene, 0.6 mL of pyridine, and 4 mLof tetrahydrofuran, and was purged with argon gas. The resulting mixturewas cooled to 0° C., to which 0.54 mL of hexanoyl chloride was addeddropwise. Thereafter, the resulting mixture was stirred for 2 hours atroom temperature. The solvent was removed from the solution underreduced pressure, followed by purifying the residues by columnchromatography, to thereby obtain 0.317 g of colorless solids.

A 25 mL-flask was charged with 0.23 g of the above-obtained colorlesssolids, 0.358 g of 4-bromomethylbenzylphosphonic acid and 4 mL of DMF,and the resulting mixture was stirred for 3 hours at 90° C. under theflow of argon gas. To the resulting reaction solution, 2-propanol wasadded to precipitate yellow solids. The yellow solids were collectedthrough filtration, and dried, to thereby obtain 0.361 g of anelectrochromic compound (Ex.-15) as yellow crystals.

Example 16

An electrochromic display element was formed using each ofelectrochromic compounds synthesized in Examples 10 to 15 in the samemanner as in Example 6. As for a counter electrode, a platinum electrodewas used. As for a reference electrode, an Ag/Ag⁺ electrode (RE-7,manufactured by BAS Inc.) was used. A cell was filled with anelectrolytic solution prepared by 0.1 M of tetrabutylammoniumperchlorate in dimethyl sulfoxide. Light was applied to the quartz cellfrom a deuterium tungsten halogen alight source (DH-2000, manufacturedby Ocean Optics, Inc.). The transmitted light was detected by aspectrometer (USB4000, manufactured by Ocean Optics, Inc.), to measurethe absorption spectrum. The absorption spectrums of the bleached stateand colored state are presented in FIGS. 8 to 13.

When the voltage of −1.5 V was applied using a potentiostat (ALS-660C,manufactured by BAS Inc.), the maximum absorption wavelength was around650 nm to around 700 nm, and the electrochromic display layer colored invivid cyan.

Comparative Example 1

The following electrochromic compound (Comp.-1) was synthesized from4,4′-bipyridine and 4-bromomethylbenzylphosphonic acid in accordancewith the method described in Example 3.

Comparative Example 2

The following electrochromic compound (Comp.-2) was synthesized from1,4-di(4-pyridyl)benzene and 4-bromomethylbenzylphosphonic acid inaccordance with the method described in Example 3.

Comparative Example 3

The following electrochromic compound (Comp.-3) was synthesized from4,4′-di(4-pyridyl)biphenyl and 4-bromomethylbenzylphosphonic acid inaccordance with the method described in Example 3.

Comparative Example 4

The following electrochromic compound (Comp.-4) was synthesized using2,7-dibromonaphthalene in accordance with the method described inExample 3.

Comparative Examples 5 to 8

Using each of the electrochromic compounds synthesized in ComparativeExamples 1 to 4, a display electrode, an electrochromic display layer,and an electrochromic display element were produced in the same manneras in (a) to (c) of Example 6. The absorption spectrums of the coloredstate of the electrochromic display elements producing using thecomparative compounds (Comp.-1), (Comp.-2), and (Comp.-3) of Comparative

Examples 1 to 3 are depicted in FIG. 14. Moreover, the absorptionspectrums of the bleached and colored states of the electrochromicdisplay element produced using the comparative compound (Comp.-4) ofComparative Example 4 are depicted in FIG. 15.

The compound (Comp.-1) and the compound (Comp.-2) depicted in FIG. 14respectively colored in blue, and in red, and the both compounds did notcolor in cyan. Regarding the compound (Comp.-3), the color associatedwith the absorption band of 450 nm was mixed the color of the absorptionband of 620 nm, and therefore the compound did not color in cyan.

Regarding the compound (Comp.-4) depicted in FIG. 15, the absorptionband of 450 nm was stronger than the absorption band adjacent to 650 nm.Therefore, the compound (Comp.-4) colored in yellow, not in cyan.

The display element, which has the electrochromic compound of thepresent invention, or the electrochromic composition, in which theelectrochromic compound is bonded to or adsorbed on an electroconductiveor semiconductive nano structure in a display layer, exhibits excellenta coloring or bleaching (coloring in cyan or bleaching the color)response to application of electric field, and also have excellent imageretentiveness (maintaining memory).

Accordingly, the electrochromic compound of the present invention iseffective for one of 3 primary colors required for realizing full-color,and the display element using such electrochromic compound is importantas technologies of a rewritable paper-like device.

The embodiments of the present invention are, for example, as follows.

<1> An electrochromic compound, which is represented by the followinggeneral formula (I):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇ and X₈ are each independently ahydrogen atom or a monovalent substituent; R₁ and R₂ are eachindependently a monovalent substituent; A⁻ and B⁻ are each independentlya monovalent anion; and Y is represented by the following generalformula (II) or (III):

where X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆, X₁₇, and X₁₈ are eachindependently a hydrogen atom or a monovalent substituent.

<2> The electrochromic compound according to <1>, wherein theelectrochromic compound is represented by the following general formula(IV):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, X₁₀, X₁₁, X₁₃ and X₁₄ are eachindependently a hydrogen atom or a monovalent substituent; R₃ is asubstituted or unsubstituted alkyl group, or a substituted orunsubstituted alkoxy group; R₁ and R₂ are each independently amonovalent substituent; and A⁻ and B⁻ are each independently amonovalent anion.

<3> The electrochromic compound according to any of <1> or<2>, wherein, in the general formula (I), R₁, or R₂, or both thereof hasa functional group capable of directly or indirectly bonding to ahydroxyl group.<4> The electrochromic compound according to <3>, wherein the functionalgroup capable of directly or indirectly bonding to a hydroxyl group isone selected from the group consisting of a phosphonic acid group, aphosphoric acid group, a carboxyl group, a silyl group, and a silanolgroup.<5> The electrochromic compound according to any of <3> or <4>, whereinthe functional group capable of directly or indirectly bonding to ahydroxyl group is one selected from the group consisting of a phosphonicacid group, a trialkoxysilyl group, and a trihydroxysilyl group.<6> The electrochromic compound according to any one of <1> to <5>,wherein A⁻ and B⁻ may be identical or different from each other, and areeach selected from the group consisting of Br⁻, Cl⁻, ClO₄ ⁻, PF₆ ⁻, andBF₄ ⁻.<7> An electrochromic composition, containing:

an electroconductive or semiconductive nano structure; and

the electrochromic compound according to any one of <1> to <6>, which isbonded to or adsorbed on the nano structure.

<8> The electrochromic composition according to <7>, wherein theelectroconductive or semiconductive nano structure is composed of metaloxide particles, and wherein the metal oxide particles are at least oneselected from the group consisting of titanium oxide, zinc oxide, tinoxide, alumina, zirconium oxide, iron oxide, magnesium oxide, indiumoxide, and tungsten oxide.

<9> The electrochromic composition according to <8>, wherein the metaloxide particles have an average primary particle diameter of 30 nm orsmaller.<10> A display element, containing:

a display electrode;

a counter electrode provided to face the display electrode and to bespaced from the display electrode;

an electrolyte provided between the display electrode and the counterelectrode; and

a display layer provided on a surface of the display electrode, whichsurface faces the counter electrode, wherein the display layer containsthe electrochromic compound according to any one of <1> to <6>, or theelectrochromic composition according to any one of <7> to <9>.

REFERENCE SIGNS LIST

-   -   1 display electrode    -   2 counter electrode    -   3 electrolyte    -   4 a electrochromic compound    -   4 b oxidation-reduction coloring section    -   4 c adsorbing group (bonding group)    -   4 d spacer section    -   4 e electrochromic composition    -   5 display layer    -   6 white reflecting layer    -   10, 20, 30 display element

1. An electrochromic compound, which is represented by the followinggeneral formula (I):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇ and X₈ are each independently ahydrogen atom or a monovalent substituent; R₁ and R₂ are eachindependently a monovalent substituent; A⁻ and B⁻ are each independentlya monovalent anion; and Y is represented by the following generalformula (II) or (III):

where X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆, X₁₇, and X₁₈ are eachindependently a hydrogen atom or a monovalent substituent.
 2. Theelectrochromic compound according to claim 1, wherein the electrochromiccompound is represented by the following general formula (IV):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, X₁₀, X₁₁, X₁₃ and X₁₄ are eachindependently a hydrogen atom or a monovalent substituent; R₃ is asubstituted or unsubstituted alkyl group, or a substituted orunsubstituted alkoxy group; R₁ and R₂ are each independently amonovalent substituent; and A⁻ and B⁻ are each independently amonovalent anion.
 3. The electrochromic compound according to claim 1,wherein, in the general formula (I), R₁, or R₂, or both thereof has afunctional group capable of directly or indirectly bonding to a hydroxylgroup.
 4. The electrochromic compound according to claim 3, wherein thefunctional group capable of directly or indirectly bonding to a hydroxylgroup is one selected from the group consisting of a phosphonic acidgroup, a phosphoric acid group, a carboxyl group, a silyl group, and asilanol group.
 5. The electrochromic compound according to any of claim3, wherein the functional group capable of directly or indirectlybonding to a hydroxyl group is one selected from the group consisting ofa phosphonic acid group, a trialkoxysilyl group, and a trihydroxysilylgroup.
 6. (canceled)
 7. An electrochromic composition, comprising: anelectroconductive or semiconductive nanostructure; and theelectrochromic compound according to claim 1, which is bonded to oradsorbed on the nanostructure.
 8. The electrochromic compositionaccording to claim 7, wherein the electroconductive or semiconductivenanostructure is composed of metal oxide particles, and wherein themetal oxide particles are at least one selected from the groupconsisting of titanium oxide, zinc oxide, tin oxide, alumina, zirconiumoxide, iron oxide, magnesium oxide, indium oxide, and tungsten oxide. 9.The electrochromic composition according to claim 8, wherein the metaloxide particles have an average primary particle diameter of 30 nm orsmaller.
 10. A display element, comprising: a display electrode; acounter electrode provided to face the display electrode and to bespaced from the display electrode; an electrolyte provided between thedisplay electrode and the counter electrode; and a display layerprovided on a surface of the display electrode, which surface faces thecounter electrode, wherein the display layer comprises an electrochromiccompound represented by General Formula (I):

where X₁, X₂, X₃, X₄, X₅, X₆, X₇ and X₈ are each independently ahydrogen atom or a monovalent substituent; R₁ and R, are eachindependently a monovalent substituent; A⁻ and B⁻ are each independentlya monovalent anion; and Y is represented by General Formula (II) or(III):

where X₉, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆, X₁₇ and X₁₈ are eachindependently a hydrogen atom or a monovalent substituent.
 11. Thedisplay element of claim 10, wherein the display layer comprises anelectrochromic composition comprising said electrochromic compound andan electroconductive or semiconductive nanostructure, wherein theelectrochromic compound is bonded to or adsorbed on the nanostructure.